As mobile electronic devices, such as a mobile phone and a laptop personal computer, are rapidly making progress, there is an increasing need to increase the capacity of a battery used in a main power supply or a backup power supply for electronic devices, and nonaqueous electrolyte batteries, such as a lithium-ion secondary battery, having a high energy density, as compared to a nickel-cadmium battery and a nickel-hydrogen battery, have attracted attention.
As representative examples of electrolyte solutions for lithium-ion secondary battery, there can be mentioned nonaqueous electrolyte solutions obtained by dissolving an electrolyte, such as LiPF6, LiBF4, LiN(CF3SO2)2, or LiCF3(CF2)3SO3, in a mixed solvent of a high dielectric constant solvent, such as ethylene carbonate or propylene carbonate, and a low viscosity solvent, such as dimethyl carbonate, diethyl carbonate, or ethylmethyl carbonate.
Further, as a negative electrode active material for lithium-ion secondary battery, a carbonaceous material capable of occluding and releasing lithium ions is mainly used, and representative examples thereof include natural graphite, artificial graphite, and amorphous carbon. For further increasing the capacity, a negative electrode of a metal or alloy using, for example, silicon or tin is also known. As a positive electrode active material, a transition metal compound oxide capable of occluding and releasing lithium ions is mainly used, and representative examples of transition metals include cobalt, nickel, manganese, and iron.
In such a lithium-ion secondary battery, the positive electrode and negative electrode having high activity are used, and therefore it has been known that a side reaction caused between the electrode and an electrolyte solution lowers the charge/discharge capacity. For improving the battery characteristics, various studies on the nonaqueous solvents and electrolytes have been made.
In patent documents 1 and 2, an attempt has been made to add an isocyanate compound to a nonaqueous electrolyte solution to improve the battery in cycle characteristics.
In patent document 3, an attempt has been made to use an electrolyte solution having added thereto lithium fluorophosphate to improve the battery in high-temperature storage characteristics.
Patent document 4 has reported that, by using an electrolyte solution having added thereto lithium fluorosulfonate, the battery is improved in high-temperature storage characteristics, input/output characteristics, and impedance characteristics.
In patent document 5, an attempt has been made to prepare a battery using a material comprising Si and O as constituent elements and a graphite material in a negative electrode active material in the negative electrode and using a halogenated cyclic carbonate or vinylene carbonate in an electrolyte solution to improve the battery in cycle characteristics.